Adjustable flow channel for an extruder head

ABSTRACT

An extruder apparatus has an extruder flow channel  10  for an extruder head having a pair of flow passages  40, 50  and a flow dam  12  interposed between the flow passages and a flow splitter  14  that locally increases or locally decreases the flow area of the first flow passage  40  relative to the second flow passage  50.  The preferred flow channel  10  adjusts the mass balance of the flows  6, 7  between passages  40, 50  automatically.

TECHNICAL FIELD

This invention relates to an apparatus for directing the flow ofelastomeric material through an extruder head.

BACKGROUND OF THE INVENTION

In the art of extruding strips of material whether they be plastic orelastomeric, the use of an extruder having a heated barrel and a screwthat provides shear energy to the material to be plasticized is wellknown. As the material is heated it generally converts from a solidpellet or strip form into a strip of plasticized material at the end ofthe screw tip that projects the material into an extruder head. Thisextruder head generally has a flow channel comprised of one or morepassages or channels that direct the plasticized material through theextruder head to an outlet or discharge die that forms the material intothe proper predetermined cross-sectional profile.

Oftentimes the extruder system is of a complex nature providing two ormore dissimilar materials to be coextruded. In one example a duplextread can be made with a top cap material and a lower base material,each material being specifically designed for its application. In evenmore complex applications, a triplex extruder can be used in which thecap material and base material also have on each lateral extreme asidewall material that is simultaneously coextruded and bonded to theother two components. All of these materials are projected into anextruder head that directs the materials into a flow channel whichassembles and bonds them so that they come out as one or more solidsingular pieces. Oftentimes it is desirable to provide adjustable flowrestricting members within these channels such that the proper amount ofmaterial is provided throughout the extrudate. Such a mechanism isdescribed in U.S. Pat. No. 5,147,195. In that patent they indicate adifficulty exists when converging streams of dissimilar rheologicalproperties that is, for instance of dissimilar viscosities andelasticities. For example, when a melt stream has a high resistance toflow relative to a melt stream which is to be converged, it may beadvantageous to provide a heavy edge flow of the high resistant meltstream prior to the convergence by using a suitable contoured streamcontacting surface. Similarly, it may be advantageous in othersituations to provide a heavy centerflow of one of the melt streamsprior to the convergence.

In U.S. Pat. No. 5,147,195, the invention is directed to providing aunique extrusion apparatus that includes a first flow channel and asecond flow channel that are separated by a divider member and whichconverge. A preferred feature of the apparatus is a segmented, flowrestricting member that provides an adjustable stream contactingsurface. The segmented flow restricting member has a face portion thatcooperate within opposing wall of the divider member to form an outputgap of one of the flow channels, an adjustment assembly is operativelyin communication with the flow restricting member and is employed toadjust the gap. These flow restricting members simply shut off a portionof the flow channel that the plasticized material is passing through,such that a volumetric change can occur in one channel or the other.While these techniques provide an adjustment capability with dissimilarmaterials such as is common in multi-material components they provide nomeans for providing a balanced flow of material when it is a homogeneousmaterial. This is particularly troublesome when elastomeric materialsare processed. In that case, the material flow is such that as therubber passes through the flow channel different flow velocities arecreated across the cross-section of the channel which will result in amass unbalance in the as-extruded profile of the component as it comesout of the extruder die. What generally happens is that one side of thedie will have the material coming out and swelling to a larger areabecause it has a higher velocity flow rate than the material on theopposite side of the die.

A further problem arises in the simultaneous extrusion of multipleprofiles from the same extruder. In this case, it is generally foundthat the mass output of each profile is not the same, even though thedie for each profile is identical. This imbalance of flow betweenmultiple cavities is related to the flow channel, and the amount ofimbalance depends on the rheological properties of the elastomericmaterial, the temperature distribution in the flow channel and flowchannel design. Furthermore, the amount of imbalance varies somewhatwhen the type of material being extruded is changed and also whenunavoidable variations in extruder operating conditions occur, such asfluctuations in temperature distribution. In the art, tool makers haveto vary the shape and cross-section of the flow channel to obtain equaloutputs of each profile. This requires repetitive machining of the flowchannel and once done for one particular elastomer material, cannot beadjusted when other types of elastomers are extruded or fluctuations inextruder operating conditions occur.

In order to compensate for these variations in flow velocities within anextruder head, there has been developed a flow channel. The flow channelof an extruder is that portion of the extruder immediately downstream ofthe screw tip and immediately upstream of the die for forming theprofile for the extruded component. These flow channels are specificallydesigned to insure that uniform flow of material occurs and that thedistribution of the material is generally uniform across the flowchannel as the material approaches the die. In order to achieve this thetoolmaker often times has to vary the shape and cross-section of theflow channel to insure that the velocity profiles approach the die in asuniform a fashion as possible. Once the flow velocities are optimized sothat they are generally uniform across the face of the die, the flowchannel is said to be balanced for that particular material. Inpractice, this requires multiple machinings of flow channels andadjustments of dies in order to achieve this balanced flow. These diesare somewhat dependent on the material being extruded, its basicrheological properties, its temperature and the velocity at which thematerial is being extruded. All of these engineering factors means thata tremendous amount of tuning is required to create a proper flowchannel for a given material being extruded and die construction.

A secondary problem that also relates to the mass and velocity imbalanceacross the die is the unwanted curvature of the extrudate after itleaves the die, such that instead of obtaining a straight strip, a“banana”-shaped curved strip is obtained. This problem is also somewhatrelated to the velocity distribution in the material as it flows throughthe flow channel. If one can visualize an extrudate coming out of a dieand it was a flat sheet, the material along the lateral edges of the diemay be moving at different velocities such that one side of the extrudedmaterial will tend to bow or bend as the other side is moving at afaster velocity, the slower side tending to stay close to the die whilethe faster moving part is moving quicker away from the die. Theresulting effect is a “banana” shaped curvature of the profiledcomponent. This curvature as the component is formed is an indicationthat the velocities of the material are dissimilar from one side of thedie to the other even though the dimensional characteristics of theprofile component may seem accurate. This non-uniform velocity changecauses the component to have a natural bow. In the preparation of tiretreads for example, this effect can have some detrimental effect on theproduct quality of the resultant tire since the accuracy with which thetread can be applied to the unvulcanized tire is reduced and anasymmetry in the molded tire, called conicity, can be created. It is,therefore, an object of the present invention to provide a flow channelthat provides a simple way of balancing the flow between multiplecavities and within each cavity so that the proper mass balance of theformed component is achieved. It is also an objective of the presentinvention to provide an adjustable means to compensate for massvariation and conicity variation within a profiled component. Whilethese features are somewhat related, each can be provided in separateflow channels or can be used in combination to achieve a proper flowchannel for the formation of elastomeric strips. In one application ofthe invention, the entire inventive concept is directed to an adjustablemass balance feature provided within a flow channel. In the secondrelated application, the flow channel is provided with an adjustableconicity weir for insuring that the profile component is provided insuch a fashion that the flow velocities do not create any conicityimbalances. While each of these features may be used separately within aflow channel and have separate utility in and of themselves, it isbelieved preferable that they be used in combination for an optimalresult. In the present application, the mass balance feature will bedescribed in detail with the conicity weir feature being provided in aseparate, but related application filed simultaneously with the presentapplication.

Where the present invention works well in balancing and providingimproved conicity of an extruded strip of elastomeric material comingout of a die with a single opening, it has been noted that thesefeatures are most beneficial when multiple components are produced froma single die having multiple openings for producing two or more stripsof material. In these cases it will be easily appreciated that massbalancing and conicity problems are exaggerated because the flow isdivided within the flow channel creating two separate flow streams thatin order to produce equal or duplicate products must have the balancematched perfectly and the conicity adjusted to insure that flowvelocities are uniform or as uniform as possible through each of the dieopenings forming the strips.

These objectives are achieved by the invention as described below.

SUMMARY OF THE INVENTION

An extruder apparatus has an extruder flow channel for an extruder headforming simultaneously one or more elastomeric strips of predeterminedcross-sectional profiles is described. The extruder flow channel has aflow inlet end of a predetermined cross-sectional area A_(i) and a firstand a second flow passage communicating with the flow inlet end and eachpassage having a flow outlet end of a predetermined cross-sectional areaA_(o) and a flow dam interposed between and separating the first flowpassage and the second flow passage. The flow dam has a flow splitter.The flow splitter locally increases or locally decreases the flow areaof the first flow passage relative to the flow area of the second flowpassage. It will be understood by those versed in the art that more thantwo extrudates can be made simultaneously by extending the concept asfollows: Four extrudates, for example, may be made by a flow channel inwhich each of the two passages described above is subdivided by damshaving flow splitters to create four separate passages.

Returning to the example with two flow passages, in use, the flowsplitter is asymmetrically oriented relative to the flow inlet end. Thisasymmetric orientation effects a difference in mass flow of theelastomeric strip in the first channel relative to the second channel.Preferably the extruder flow channel has a mass flow sensor in eachfirst and second flow passage or on each elastomeric strip.

Most preferably the extruder head flow channel has a flow splitteradjustment mechanism attached to the flow splitter. The flow splitteradjustment mechanism moves the flow splitter during the operation of theextruder to effect a relative change in the flow area of the first flowchannel relative to the flow area of the second flow channel. Theextruder flow channel preferably has the mass flow sensor in each firstand second flow channel, a logic circuit connected to the sensors tomeasure the difference in mass flow and to calculate the amount anddirection the mass flow splitter must move to equalize flow, a means forsignaling the amount of flow splitter adjustment, an actuator for movingthe flow splitter adjustment mechanism by a predetermined amountrequested by the means for signaling. Preferably, the mass flow sensorsare located down stream of the mass flow splitter. Additionally, themass flow sensors signal total mass flow values in each channel to thelogic circuit which can calculate the total mass flow to a means forsignaling the extruder to increase or decrease extrudate flow. In thisway, not only can mass flow differences between the first and secondchannels be detected, but also the delivery amount of extrudate can beadjusted.

In the preferred embodiment the mass flow splitter has a substantiallytriangular cross-section having an apex. The apex is in proximity to theflow inlet end, preferably in very close proximity to the flow inletend. The mass flow splitter is preferably pivotally movable relative tothe dam.

In the preferred embodiment each first and second flow passage tapersinwardly in one direction and widens in another direction below theinlet end to the outlet end forming a substantially trapezoidal portionadjacent the outlet end. In each of the trapezoidal portions, there isincluded a flow weir in each flow passage. In an example, the weir has asubstantially triangular shape extending to a height less than the fulldepth of the channel. Preferably the weirs height reaches a peak of atleast 50% of the flow channel depth and is provided to effect aredistribution of the elastomeric flows mass prior to entering the finalshaping die of the extruder head.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a top plan view of the extruder flow channel connected toan extruder on the upstream side of the material flow and to a profilingdie on the downstream side of the channel flow.

FIG. 2 is an end view of the cross-section taken from FIG. 1 along lines2—2.

FIG. 3 is an exemplary finished die forming an elastomeric strip havinga single opening.

FIG. 4 is an exemplary die having two profile openings forming twoelastomeric strips of similar cross-sectional profile.

FIG. 5A shows an improperly balanced flow channel.

FIG. 5B shows the ideal flow velocity balance obtained by adjusting theflow splitter.

FIG. 6 shows the flow velocity prior to contacting the flow weirs.

FIG. 6A shows an improperly balanced flow velocity of an extruded stripas it leaves the die.

FIG. 6B is the ideal flow velocity of a formed component as it leavesthe finished die.

FIG. 7 is a cross-sectional view of an elastomeric strip.

FIG. 8 is a cross-sectional view of the flow splitter adjustmentmechanism.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIGS. 1 and 2 an extruder is commonly known in the artand not illustrated has an extruder screw 2 having an extruder tip 4enclosed in an extruder barrel 3. Attached to the extruder barrel is anextruder head 5. The extruder head includes a flow channel 10 which hasan inlet end 30 for accepting plasticized material preferablyelastomeric material and an outlet end 32 for discharging theplasticized material through a die for forming the profile of theelastomeric strip to be produced. This die is commonly referred to as aprofile die 60 while the elastomeric strip is item 20 as illustrated inFIG. 7.

Between the inlet end 30 and the outlet end 32 of the flow channel 10,there are first and second flow passages 40, 50 respectively. Interposedbetween the first and second flow passages 40, 50, is a flow dam 12. Theflow dam 12 separates the first flow passage 40 from the second flowpassage 50. At the very tip of the flow dam is a mass flow splitter 14.As shown, the mass flow splitter has an apex 15. As illustrated the massflow splitter has a substantially triangular shape with the apex 15being in the “neutral” position symmetrically oriented relative to theflow inlet end 30. The flow splitter locally increases or locallydecreases the flow area of the first flow passage 40 relative to theflow area of the second flow passage 50 by being asymmetrically orientedrelative to the flow inlet end 30. This asymmetric positioning of theflow splitter 14 relative to the mass flow insures that the rubber as itflows from the inlet area A_(i) is redistributed volumetrically. Thisasymmetric positioning of the apex of the mass flow splitter 14restricts one of the flow passages 40, 50 more than the other flowpassages 40, 50 thus creating a localized back pressure thatredistributes the mass of the rubber on each of the first and secondflow channels. By properly selecting the amount of shift in the apex 15of the flow splitter 14 relative to the inlet cross-sectional areaA_(i), one is able to effectively balance the amount of rubber massflowing through each passage 40, 50 so that they are approximately equalin pounds mass of rubber being transferred through each flow passage 40,50. While this feature is beneficial in producing a single elastomericstrip 20 from a profile die 60 as illustrated in FIG. 3, it is even morebeneficial in producing multiple strips 20 from a single die 60 asillustrated in FIG. 4, wherein the die has two openings 62 for formingtwo strips simultaneously, one being formed from each flow passage 40,50 as the rubber mass is being distributed through the flow passages andthe profile die 60. As the dam 12 extends towards the outlet end 32 ofthe flow channel 10, it converges back to a discharge apex 16 asillustrated. As can be seen in FIG. 2, the dam 12 and the channels 40,50 taper inwardly. The passages 40, 50 elongate laterally so as toflatten the cross-sectional area as the elastomeric flow approaches thedischarge end 32 of the flow channel 10 and prior to entering into theextruder profile die 60. Although not required, the dam 12 can extendalmost the full length W of the flow channel 10 creating a blockage andcompletely separating the first flow passage 40 from the second flowpassage 50 at the discharge end 32.

With reference to FIGS. 5A and 5B, the flow velocity vector profile inthe flow channel 10 is shown in an unbalanced condition, with the fasterflow occurring in passage 40 in this example FIG. 5A. A certainunbalance is typical in a symmetric flow channel design. This unbalancedcondition can be eliminated by orienting the flow splitter 14 to reducethe flow area in the passage experiencing faster flow. In the exampleshown in FIG. 5A, the condition is corrected by orienting the apex ofthe flow splitter onto passage 40, as shown in FIG. 5B.

At the discharge end 32 of the flow channel 10, there is illustrated inFIG. 1 a first flow weir 22 in the first flow passage and a second flowweir 24 in the second flow passage 50. As illustrated, these flow weirs22, 24 are asymmetrically positioned within the flow channel, each flowweir is substantially triangular in shape having an apex portion 25 atthe leading end, the apex portion creating a mass flow diverter 28.

As shown in FIG. 5B as the elastomeric flow leaves the extruder barrel 3and enters the inlet 30 of the flow channel 10, the mass flow isseparated into two portions 6,7, each portion 6, 7 has a distinctvelocity profile of the rubber as it is flowing through the flowpassages 40, 50, respectively. As the rubber 20 impinges the flow weirs22, 24 at the mass flow diverter 28 at the leading end of the weirs, thevelocity profile is flattened with the objective being that the rubberas it enters the extruder die at the outlet end of the flow channel hasa velocity profile that is substantially constant across the laterallength of the die. As illustrated in FIG. 2 each weir 22, 24 extends toa height that is less than the full depth of the passages 40, 50 at thelocation where the weirs 22, 24 are positioned. Preferably the weirs 22,24 occupies 40 percent or more of the full depth of the flow passages40, 50 in the area where the mass flow diverter is located.

It is believed important that the apex 25 of the weirs 22, 24 bepositioned so that it impinges normal to the velocity profile of theflowing elastomeric strip 20 within each respective passage 40, 50. Asshown, the material 20 impinges the flow weirs 22, 24 upon an angularflow and, therefore, it is believed important that the flow weirs 22, 24be asymmetrically positioned to insure that they intercept at themaximum flow velocity within the flow channel as shown in FIG. 5B. Ifthe flow channel 10 is provided such that velocity profile of theelastomeric flow in each flow passage 40 and 50 is symmetrical, then itis presumed that the flow weirs could be positioned symmetrically withinthe flow channel because in that construction the maximum flow velocitywould be presumed to be at the midpoint of the flow passages 40, 50 orin close proximity thereto. As illustrated in FIG. 1, however, the flowis moving at a slight angular orientation to the die discharge end 32and this means that the material mass of the rubber 20 closest to thedam 12 should be moving at a higher velocity because it has a shorterdistance to travel to reach the discharge end 32. Accordingly, it isbelieved important for the apex of the flow diverter 28 to be locatedcloser to the dam 12 at the point where the maximum flow velocity isoccurring as illustrated in FIGS. 1 and 5. The mass flow splitter 14 isattached to the dam 12 and a mass flow diverter 28 attached to both thefirst weir 22 and the second weir 24. Each can be rigidly mounted andnonmovable relative to the flow path. This can be accomplished byfastening the flow splitter 14 and the mass flow diverters 28 directlyto the flow channel 10. When this is done, the location of the apex 15,25 or leading end of each component 12, 22, 24 must be preselected in afashion to determine the optimal location. Assuming that the mass flowis not correctly balanced, or that there is a conicity problem with theformed strip 20, then an adjustment can be made to the angularorientation of the apex 15, 25 shifting it either slightly to one sideor the other of the passages 40, 50, thereby opening or restricting theflow in the passages or diverting the flow at the weirs 22, 24. Thismethod of adjusting and balancing the flows is done in an empiricalfashion requiring an inventory of these components 14 and 28, eachhaving different apex angles. Conicity or mass imbalance irregularitiesare corrected by exchanging components with those in the inventory. Asone skilled in the art can easily appreciate this iterative process canbe somewhat time consuming although preferable over the current art.

It is accordingly preferred, therefore, that the mass flow splitter 14and the mass flow diverters 28 be movable within the channels 40, 50 asthe material 20 is flowing. In this fashion, if these elements arepivotally movable relative to the channel then immediate adjustments canbe made on a real time basis assuming adequate sensors and logiccircuits are available to measure, analyze and request the necessaryadjustment thereby restricting or opening the flow in the channels 40,50 as it is needed to create the necessary balance or conicityadjustment.

The flow splitter adjustment mechanism 35 illustrated in FIG. 8 includesan actuator 36 which can move the flow splitter 14 about a pivot pin 17,thereby shifting the apex 15 relative to the inlet area A_(i) andredirecting a portion of the flow 6, 7 in one side of the channel 40 orthe other side of the channel 50 as need be. As illustrated, these arepreferably achieved by providing a sensor means 80 in each flow channels40, 50 that would measure the amount of mass flow 6, 7 being transferredthrough the flow channels 40, 50 and send a single back to a logiccircuit 90 which would analyze the data and direct the actuator 36 tomove the pivoted pin 17 a predetermined amount to adjust the apex 15 ofthe flow splitter 14 relative to the flow channels openings 40, 50.

Similarly the type of same mechanism will be used on the mass flowdiverters 28 within each weir 22, 24, each would have a pivot pin 17, anactuator 36 and a mass flow adjustment mechanism 34 for enabling themass flow diverter 28 to be pivotally rotated relative to the flowchannels 40, 50 thereby adjusting the mass flow velocities to preventany downstream conicity problems from occurring.

By providing this type of mechanism with internal sensing 80, it willenable the mass flow channels 40, 50 to be automatically adjusted inreal time compensating for any variations within the extrudate flows 6,7 as it is leaving the profile die 60. Additionally, it is believeddesirable that the mass flow sensors 80 provide a signal back to thelogic circuit 90 that would also communicate with the extruder mechanism1 which could increase or decrease the amount of total mass flow beingdischarged at the inlet end 30 of the flow channel 10. In this way, thetotal mass can be varied as the extrudate being formed.

Alternatively, one could simply measure the profile of the extrudedcomponent strips 20 and weigh it as it is being formed in such a fashionto provide the necessary feed-back mechanism. This alternative way ofmeasuring while fairly easy to accomplish does have some inherent lagtimes with regard to correcting conicity and mass imbalances, and,therefore, is considered to be somewhat less desirable then the realtime measurements occurring within the flow channels 40, 50 themselvesas illustrated.

With reference to FIGS. 6A and 6B, one will see that the flow weirs 22,24 at the outlet end or discharge end 32 of the flow channels 40, 50create a velocity vector profile of the elastomeric or rubber flows 6,7. As illustrated in 6A, that profile shows an increased velocityclosest to the dam 12. By pivoting the mass diverter 28 on the weir 22,there is a constriction in the flow closest to the dam 12. Thisconstriction effectively slows the mass flow 6 close to the dam 12 andpermits the velocity profile to flatten so that in the most preferredembodiment a uniform velocity vector profile is exhibited as theextrudate approaches the forming die 60.

What is claimed is:
 1. An extrusion apparatus having an extruder flowchannel for a extruder head forming simultaneously one or moreelastomeric strips of predetermined cross-sectional profiles, theextruder flow channel comprising: a flow inlet end of a predeterminedcross-sectional area A_(i); a first and a second flow passagecommunicating with the flow inlet end and each passage having a flowoutlet end of a predetermined cross-sectional area A_(a); a flow daminterposed between and separating the first flow passage and the secondflow passage, the flow dam having a flow splitter end in proximity tothe inlet end; a pair of weirs, a first weir being located in the firstflow passage in proximity to the first outlet end, a second weir beinglocated in the second flow passage in proximity to the second outletend, each first and second weir having a mass flow diverter at a leadingend of the weir, wherein each mass flow diverter is movable relative tothe flow path within the passage.
 2. The extrusion apparatus of claim 1wherein the mass flow diverter of each weir is oriented asymmetricallyrelative to the mass flow within each passage as measured relative tothe direction of the mass flow.
 3. The extrusion apparatus of claim 1further comprising: a mass flow diverter adjustment mechanism attachedto the mass flow diverter, the mass flow diverter adjustment mechanismmoves the mass flow diverter to effect a relative change in the flowarea of the respective passage in proximity to the respective outletend.
 4. The extrusion apparatus of claim 3 further comprising a profileforming die attached to the outlet ends of the extruder flow channel,the profile forming die having two or more openings, said openingforming elastomeric strips of a predetermined cross-section.
 5. Theextrusion apparatus of claim 4 further comprising a sensor for measuringthe conicity variation of the formed strip; a logic circuit to receive asignal from the sensor and to calculate the adjustment needed toeliminate the conicity variation at the mass flow diverter, an actuatorfor moving the mass flow diverter adjustment mechanism by apredetermined amount as calculated by the logic circuit.
 6. Theextrusion apparatus of claim 1, wherein the mass flow diverter of eachweir is removable from the flow channel and interchangeable with othermass flow diverters having different apex angles, chosen from aninventory of mass flow diverters whose angles collectively cover a widerange.